EEE-Masterclass Series

Material

Chapter 1

Gaseous Detectors working principles

For this part we provide some slides (click here to download the slides). In there you can find a detailed explanation of the working principles of the gas filled detectors.

The following sections provides the basic elements to tackle the exercises.

If you have any questions please contact marco.garbini@cref.it.

Chapter 2

How is the efficiency defined?

The efficiency of the detector is defined as the fraction between the number of detected particles crossing the detector and the total number of particles detected by it.

So usually we need to know the number of particles crossing the detector under test and measure the number of particles that we actually reveal. We typically use two detectors placed above and below the detector we want to study.

To measure the efficiency we count the number of particles crossing the two reference detectors in a certain time (we call this value DEN) and while simultaneously counting the number of particles detected by all the three detectors (we call this value NUM). So the efficiency of our detector will be:

Eff= (NUM/DEN)

The detector efficiency is a function of the applied High Voltage. The efficiency increases with the applied voltage till a plateau that represents the region where the detector is stable. Ideally we want to work with detectors that are 100% efficient; our MRPCs are close to this value of efficiency for High Voltage greater than 17000 V. Of course another fundamental ingredient is the gas that is used (see Chapter 1 for the details).

The typical efficiency curve for our detectors is shown in the picture below. We can observe how the efficiency increases as the applied High Voltage increases.

It is useful to express the applied High Voltage normalizing it to reference Pressure and Temperature. We call it HV_effective or HV_eff and it is given by the formula:

HV_eff=HV(P_0/P)*(T/T_0)

where, HV is the applied High VOltage in V, P_0 is the reference pressure in mbar (we use 1010 mbar), P is the pressure measured at the detector site, T_0 is the reference temperature in K (we use 293.15 K), T is the temperature in K at the detector site.

The study of the efficiency curves with different gas mixtures and at different environmental conditions is the goal of the following section.

Chapter 3

Efficiency Curves

Use the following exercises to compare the detector response as function of High Voltage and gas mixture.

EXERCISE 1

The first part of the Master Class is dedicated to the study of the efficiency curves of 2 EEE Telescopes. You can find the data at the link:

https://docs.google.com/spreadsheets/d/1Q_4T3GVYH_WPQ2eeSdjoq26IzjwR1rClGy9KHf-3Lxg/edit?usp=sharing

(DOWNLOAD THE FILE OR CREATE YOUR OWN COPY)

The data are organized in the following way:

The first column reports the name of the telescope (BOLO-01 and then CERN-01) followed by the columns reporting respectively the High Voltage, the pressure, the temperature , the efficiency and its error. The last column is used for notes and comments.

At the link

https://docs.google.com/spreadsheets/d/1JrjV-j9YYGc-Bl6tkQUiONUAW6wXcxc4cvEW4s7_QmI/edit?usp=sharing

(DOWNLOAD THE FILE OR CREATE YOUR OWN COPY)

you can find the data related to the measurement of the efficiency of the bottom chamber of the telescope at an High Voltage of 17000 V (in this case we don't care about the P and T corrections).

The data are organized as follows:

For each chamber you can find the x,y coordinate (in cm) of the passing particle and the time (in ns) the event is recorded with respect to a T_zero. The 3 chambers are at the vertical distance of 50 cm form each other.

We will use these data to measure the efficiency using different selection criteria to identify real particles from not physical signals.

Step 1:

Count the number of events with signal in both the top and middle chamber (this number is "DEN" of the above formula) and count the events detected by all the three chambers ("NUM" in the above formula) and compute the efficiency as NUM/DEN. (HINT)

Step 2:

Can you compute where is the signal expected (x,y,T) on the middle chamber on the basis of the distance between the chambers (50 cm) and the measure on the top and middle chamber?

Try to calculate the BOT extrapolation.

We will use this extrapolation to refine the efficiency evaluation during the classroom!